CLA SSIFICA TION OF IGNEO US RO CKS 6 4 I 



porphyritic basalts, diabases, and other lavas known by a num- 

 ber of names, which before the classic studies of Zirkel were 

 grouped togther as basalt. 



B. Porphyry — porphyritic forms may all be embraced within 

 the general term of porphyry. They may be separated on a 

 basis of color to correspond to the divisions above mentioned 

 into two groups. 



1. Leucophyre (Giimbel, 1874) and 



2. Melaphyre (Brongniart, 18 13). 



Giimbel applied the term leucophyre to certain altered dia- 

 bases of light color, which would not be included within the 

 group here proposed, but the term was applied to altered rocks 

 and has never been in general use, and may advantageously be 

 redefined. 



Leucopliyres would include all porphyritic, aphanitic, igneous 

 rocks, with light-colored groundmass, and with phenocrysts of 

 any kind. 



Melaphyres would include all porphyritic, aphanitic igneous 

 rocks with dark-colored groundmass, and with phenocrysts of 

 any kind. 



According to the kinds of phenocrysts which may be identi- 

 fied megascopically these rocks may be named without reference 

 to the color of the groundmass as : 



Qtiartz-porphyry or quartzophyre . 



Feldspar-porphyry or feldsparphyre, but not felsophyre, since 

 this name is in common use for a porphyry with felsitic ground- 

 mass. 



Hornblende -porphyry or hornblendophyre . 



Mica-porphyry or micaphyre. 



Augite porphyry or angitophyre (von Buch, 1824). 



Olivine-porphyry or olivinopliyre (Vogelsang, 1872). 



If it is intended to indicate the color of the groundmass as 

 light or dark, we may use the terms : 



Quartz-leucophyre or quartz-?nelaphyre . 



Feldspar-leucophyre or feldspar-?nelaphyre . 



Hornble?ide- leucophyre or hornblende -melaphyre . 



